Indoor air can include trace amounts of contaminants: e.g., dust, smoke, carbon monoxide, as well as volatile organic compounds generated or outgassed from the living space as a byproduct of our modern building methods. Particular offenders among these are the adhesives used for installation of carpets, flooring, insulation, etc. As indoor air flows through the return ducts of a heating, ventilation and air conditioning (HVAC) system, the air first encounters the system air filter which blocks the passage of particulate contaminants, and allows the return air to enter the portion of the HVAC system where it is heated, cooled, humidified, or dehumidified. A drawback to employing filters is that they simply block the passage of particulate contaminants and do not destroy them. However, they are essential in removing particulate contaminants from the air prior to conditioning.
It is known to use ultraviolet (UV) radiation alone in HVAC systems to kill airborne bacteria and viruses. Additionally, photocatalytic oxidation (PCO) air purification systems employ a photocatalytic coating, e.g., titanium dioxide, in combination with an activating photonic light source of a particular wavelength to destroy indoor airborne contaminants including volatile organic compounds such as formaldehyde, toluene, propanal, butene, and acetaldehyde. The system arrangement commonly includes one or more ultraviolet lamps, and a photocatalytic monolith, such as a honeycomb, coated with the photocatalytic coating. Titanium dioxide is well known as a photocatalyst in a fluid purifier to destroy such contaminants. When the titanium dioxide is illuminated with UV light, photons are absorbed by the titanium dioxide, promoting an electron from the valence band to the conduction band, thus producing a hole in the valence band and adding an electron in the conduction band. The promoted electron reacts with oxygen, and the hole remaining in the valence band reacts with water, forming reactive hydroxyl radicals. When a contaminant adsorbs onto the titanium dioxide photocatalyst, the hydroxyl radicals attack and oxidize the contaminants to water, carbon dioxide, and other substances.
UV lamps in PCO applications are customarily tubular in form, and emit ultraviolet-wavelength photons within 360° around the longitudinal axis of the lamps. While UV light is extremely useful in the air purification and PCO applications, UV light is also very harmful to certain materials commonly found in the HVAC system, e.g., the air filter, electrical insulation, other polymers, etc. Exposure of these components to UV radiation results in early degradation and decreased system performance.
Accordingly, what is needed in the art is a device that protects vulnerable system components from UV light while not interfering in the air purification and PCO applications.